Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/1323—Arrangements for providing a switchable viewing angle
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
  • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/30—Collimators
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1676—Electrodes
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1677—Structural association of cells with optical devices, e.g. reflectors or illuminating devices
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1679—Gaskets; Spacers; Sealing of cells; Filling or closing of cells
  • G02F1/1681—Gaskets; Spacers; Sealing of cells; Filling or closing of cells having two or more microcells partitioned by walls, e.g. of microcup type
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1685—Operation of cells; Circuit arrangements affecting the entire cell
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/004—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/02—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light
  • G02B26/026—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light based on the rotation of particles under the influence of an external field, e.g. gyricons, twisting ball displays
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/136—Liquid crystal cells structurally associated with a semi-conducting layer or substrate, e.g. cells forming part of an integrated circuit
  • G02F1/1362—Active matrix addressed cells
  • G02F1/1368—Active matrix addressed cells in which the switching element is a three-electrode device
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
  • G02F2201/44—Arrangements combining different electro-active layers, e.g. electrochromic, liquid crystal or electroluminescent layers

Definitions

• This invention relates to switchable light-collimating films that can be used, e.g., to control the directionality of incident light passing through a transparent or translucent substrate.
• Passive films that have this ability have been commercially-available for some time, and are widely-sold for use as“privacy filters” for computer monitors. See, e.g., offerings from 3M Corporation, St. Paul, MN, as well as various US patents, such as US 8,213,082.
• a privacy filter is applied to the front surface of a video display when the user wants to limit the images on the display to a“privacy cone” that is only viewable by the user.
• Privacy films typically employ microfabricated channels of plastic that are backfilled with materials having a different index of refraction from the plastic substrate.
• the interface between materials creates a refractive surface and only light that is oriented in the correct direction will pass through the filter, while other incident light that is oriented in the incorrect direction will be back-reflected and/or absorbed.
• This same technology can also be used as a window treatment to modify the directionality of, e.g., sunlight passing through an exterior window.
• U.S. Patent Publication 2016/0179231 (‘231 Application) describes an electroactive privacy layer that can be used in conjunction with a display device.
• The‘231 Application teaches to use an electrically-anisotropic material, such as a dielectric polymer. When an electric field is applied, the anisotropic material is aligned with the field, collimating the light and providing a zone of privacy for the user. However, it is necessary to provide a constant electric potential to the privacy layer to keep the material aligned to maintain the privacy state.
• PCT Publication WO2013/048846 also describes an alternate switchable privacy film that also employs anisotropic particles that are held in an aligned position with an electric field. Similar to the‘231 Application, devices of the‘846 publication also require constant energy to be supplied in the privacy state.
• this invention describes voltage waveforms for driving a light-collimating film that includes a plurality of elongated chambers of bistable electrophoretic fluids including light-scattering pigments.
• the films can provide a 2x narrowing (or more) of viewing angle to light passing through the film.
• the light-collimating films include bistable electrophoretic fluids, the light collimating films are stable for long periods of time in the wide or narrow states, and only require energy to change from one state to the other.
• the bistable electrophoretic fluid is partitioned into a plurality of elongated chambers, the electrophoretic materials are less susceptible to settling when the same light-collimating film is applied in different orientations with respect to gravity. Additionally, the transition speed between wide and narrow states is improved, and the overall effect is more consistent across a device when the bistable electrophoretic fluid is partitioned into many elongated chambers.
• the light-collimating film includes a plurality of small chambers, it is easy to cut the film to the desired shape/size after fabrication without losing large amounts of electrophoretic fluid.
• a square meter section sheet of light-collimating film or a roll of light-collimating film can be cut into chips of desirable size without significant loss of electrophoretic fluid.
• each chamber holds only a small amount of fluid, so the overall loss is small.
• hundreds of small sheets e.g., for mobile phones
• the elongated chambers can be fabricated with a pre-determined pattern such that sheet cutting results in no loss of electrophoretic fluid.
• the invention includes a method for driving a switchable light- collimating film, wherein the switchable light-collimating film includes a first light- transmissive electrode layer, a collimating layer having a thickness of at least 20 pm comprising a plurality of elongated chambers, and a second light-transmissive electrode layer, wherein the first and second light transmissive layers are disposed on either side of the collimating layer.
• Each elongated chamber has an opening and a bistable electrophoretic fluid comprising pigment particles is disposed in each elongated chamber.
• the elongated chambers are sealed with a sealing layer that seals the bistable electrophoretic fluid within by spanning the opening of the elongated chamber.
• the method includes applying a time varying voltage between the first and the second light-transmissive electrode layers.
• the switchable light-collimating film typically has a thickness of less than 500 pm, and the height of the elongated chambers is equal to or less than the thickness of the collimating layer.
• the elongated chambers are between 5 pm and 150 pm in width, and between 200 pm and 5 mm in length.
• the elongated chambers can be between 5 pm and 50 pm in width, and between 50 pm and 5 mm in length.
• the switchable light-collimating film is typically made from a polymer, for example a polymer made from acrylate monomers, urethane monomers, styrene monomers, epoxide monomers, silane monomers, thio-ene monomers, thio-yne monomers, or vinyl ether monomers .
• the first or second light-transmissive electrode layers may be made from indium- tin-oxide.
• the bistable electrophoretic fluid typically includes polymer-functionalized pigment particles and free polymer in a non-polar solvent. Often, the pigment is functionalized with a polyacrylate, polystyrene, polynaphthalene, or polydimethylsiloxane.
• the free polymer may include polyisobutylene or copolymers including ethylene, propylene, or styrene monomers
• the sealing layer may include a water soluble polymer or water dispersible polymer, such as naturally-occurring water-soluble polymers, such as cellulose or gelatin, or synthetic polymers, such as polyacrylate, a polyvinyl alcohol, a polyethylene, a poly( vinyl) acetate, a poly( vinyl) pyrrolidone, a polyurethane, or a copolymer thereof.
• the time varying voltage includes a first voltage for a first time that has a first polarity and a second voltage for a second time that has a second polarity.
• the first voltage has a first magnitude
• the second voltage has a second magnitude
• the first and second magnitudes are not equal.
• the first voltage has a first magnitude
• the second voltage has a second magnitude
• the first and second magnitudes are not equal.
• the product of the first voltage and the first time is a first impulse
• the product of the second voltage and the second time is a second impulse
• the first impulse and the second impulse are not equal in magnitude.
• the product of the first voltage and the first time is a first impulse
• the product of the second voltage and the second time is a second impulse
• the first impulse and the second impulse are equal in magnitude
• the time varying voltage further includes the first voltage for a third time that has the first polarity and the second voltage for a fourth time that has the second polarity.
• the time varying voltage is between 5 V and 150 V in magnitude, e.g., between 80 V and 120 V.
• the elongated chambers are arranged in rows and columns when the collimating layer is viewed from above, wherein the longer dimension of the elongated chambers run along rows, and wherein the rows are separated from each other by at least three times the width of the elongated chambers.
• the elongated chambers are arranged in rows and columns when the collimating layer is viewed from above, and the adjacent elongated chambers within the same row are separated by a gap of less than 30 pm.
• the gaps between adjacent elongated chambers in the first row are offset horizontally from the gaps between adjacent elongated chambers in the second row.
• the symmetry of the elongated chambers is disrupted by altering the length of the elongated chambers, the width of the elongated chambers, the pitch of the elongated chambers, or the width or placement of the gap between elongated chambers.
• the invention includes a display having a light source, a switchable light-collimating film, an active matrix of thin film transistors, a liquid crystal layer, a color filter array, a voltage source, and a controller.
• the switchable light-collimating film includes a first light-transmissive electrode layer, a collimating layer having a thickness of at least 20 pm comprising a plurality of elongated chambers, and a second light-transmissive electrode layer, wherein the first and second light transmissive layers are disposed on either side of the collimating layer.
• the elongated chambers hold a bistable electrophoretic fluid comprising pigment particles and the elongated chambers are sealed with a sealing layer that spans the opening of the elongated chamber.
• the controller provides a voltage impulse between the first and second light-transmissive electrode layers, wherein the voltage impulse causes a change in the effective transmission angle of the display.
• the light-collimating film or display additionally include a voltage source and a controller to provide a voltage impulse between the first and second light- transmissive electrode layers.
• the display includes a prism film disposed between the light source and the switchable light-collimating film.
• the display includes a diffusion layer between the prism film and the light source.
• the display includes a touch screen layer.
• FIG. 1A illustrates a first state of a switchable light-collimating film in which electrophoretic particles are distributed throughout the chambers of a collimating layer. The electrophoretic particles are stable in this state without the application of power.
• FIG. 1B illustrates a second state of a switchable light-collimating film in which electrophoretic particles are driven toward a first light-transmissive electrode with the application of an electrical potential.
• FIG. 1C illustrates a third state of a switchable light-collimating film in which electrophoretic particles are collected in proximity to the first light-transmissive electrode. The particles are stable in this position even after the electric potential has been removed.
• FIG. 1D illustrates a return to a state in which the electrophoretic particles are distributed throughout the chambers of a collimating layer.
• FIG. 1E illustrates a fourth state of a switchable light-collimating film in which electrophoretic particles are driven toward a second light-transmissive electrode with the application of an electrical potential having an opposite polarity of FIG. 1B.
• FIG. 1F illustrates a fifth state of a switchable light-collimating film in which electrophoretic particles are collected in proximity to the second light-transmissive electrode. The particles are stable in this position even after the electric potential has been removed.
• FIG. 2A illustrates that when electrophoretic particles are distributed throughout chambers of a collimating layer, rays of light emitted from a source are limited to an angle qh
• FIG. 2B illustrates that when electrophoretic particles are collected against a light- transmissive electrode closest to the light source, rays of light emitted from the source at an angle q 2 , wherein q 2 » q i .
• FIG. 2C illustrates that when electrophoretic particles are collected against a light- transmissive electrode furthest from the light source, rays of light emitted from the source at an angle q 3 , wherein q 3 » q i . It is observed that there is minimal light loss due to the presence of the pigment particles at the emissive side of the light-collimating film.
• FIG. 3 A illustrates simple waveforms that can be used to switch a light-collimating film between a first state and a second state.
• FIG. 3B illustrates complex waveforms that can be used to switch a light- collimating film between a first state and a second state.
• FIG. 4 illustrates the operative layers of a liquid crystal display assembly including a switchable light-collimating film. The layers are not to scale.
• FIG. 5 A illustrates the effective viewing angle, cp, of an LCD display stack including a light-collimating layer when the electrophoretic particles are dispersed in the elongated chambers. Note that Viewer #2 does not“see” much of the light from the LCD display stack.
• FIG. 5B illustrates the effective viewing angle, cp, of an LCD display stack including a light-collimating layer when the electrophoretic particles are packed at the bottom (or top) of the elongated chambers.
• FIG. 5C illustrates the intensity of light as a function of effective viewing angle when an LCD display stack including a light-collimating layer is in the first state (see FIG. 5 A) and the second state (see FIG. 5B).
• FIG. 6 illustrates an embodiment of a switchable light-collimating film disposed on a lower substrate.
• the switchable light-collimating film additionally includes an edge seal.
• the exploded view details the sealing layer atop the elongated chamber filled with bistable electrophoretic fluid.
• FIG. 7 illustrates a switchable light-collimating film that has an optically clear adhesive and a release sheet on one side. Such films may be used, for example, to provide collimating features on existing surfaces, such as a glass windows.
• FIG. 8 illustrates a roll-to-roll process that can be used for forming a collimating layer with a plurality of elongated chambers and subsequently filling the elongated chambers with a bistable electrophoretic fluid and sealing the filled elongated chambers.
• FIGS. 9 A and 9B illustrate a simplified embossing process.
• FIG. 10 details a method for forming an embossing tool to create collimating layers of the invention.
• FIG. 11 details a method for forming a shim to be used in an embossing tool.
• FIG. 12 details an alternate method for forming a shim to be used in an embossing tool.
• FIG. 13 is a top view of an embodiment of a switchable light-collimating film in which elongated chambers are arranged in a row-column format.
• FIG. 14 is a top view of an embodiment of a switchable light-collimating film in which elongated chambers are arranged in a row-column format.
• the present invention provides driving waveforms for a light- collimating film that includes elongated chambers of bistable electrophoretic fluids.
• Such films can be used, on their own, to control the amount and/or direction of light incident to a transmissive substrate.
• Such films can also be integrated into devices, such as an LCD display, to provide useful features such as a zone of privacy for a user viewing the LCD display.
• the collimation of the emitted light can be altered on demand.
• the collimation state will be stable for some time, e.g., minutes, e.g., hours, e.g., days, e.g., months, without the need to provide additional energy to the light-collimating film.
• the systems described herein can be fabricated inexpensively using roll-to-roll processing. Accordingly, it is feasible to produce large sheets of switchable light-collimating film that can be incorporated into devices during other assembly processes, such as the fabrication of an LCD display.
• Such films may include an auxiliary optically-clear adhesive layer and a release sheet, thereby allowing the light-collimating film to be shipped and distributed as a finished product.
• the light-collimating film may also be used for after-market light control, for example for conference room windows, exterior windows in buildings, and sunroofs and skylights.
• the first and second electrodes of the light-collimating films are easily accessed, using for example laser cutting, so it is quite easy to connect a voltage source and controller to the electrodes.
• An electrophoretic display normally comprises a layer of electrophoretic material and at least two other layers disposed on opposed sides of the electrophoretic material, one of these two layers being an electrode layer.
• both the layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display.
• one electrode layer may be patterned into elongate row electrodes and the other into elongate column electrodes running at right angles to the row electrodes, the pixels being defined by the intersections of the row and column electrodes.
• one electrode layer has the form of a single continuous electrode and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines one pixel of the display.
• two light-transmissive electrode layers are used, thereby allowing light to pass through the electrophoretic display.
• FIGS. 1A-1F The general function of a switchable light-collimating film (10) is shown in FIGS. 1A-1F.
• the film (10) includes first (12) and second (14) light-transmissive electrode layers. Typically, each electrode layer is associated with a first substrate (16) and a second substrate (18), respectively.
• the first (16) and second (18) substrates may be a light-transmissive polymer (e.g., a film or resin) or glass. In the instance that the film (10) is produced with roll- to-roll processing, the first (16) and second (18) substrates are flexible.
• the light-transmissive electrodes and the substrates may also be integrated into a single layer, for example a PET-ITO film, PEDOT, or another light-transmissive polymer that is doped with a conductive material (e.g., graphene, nanotubes, metal flakes, conductive metal oxide particles, or metal fibers) and/or doped with conductive monomers or polymers and/or doped with ionic materials, such as salts.
• a conductive material e.g., graphene, nanotubes, metal flakes, conductive metal oxide particles, or metal fibers
• ionic materials such as salts.
• the light-collimating layer (21) comprises a light-transmissive polymer (20) that has been processed to produce a plurality of elongated chambers (22) to hold a bistable electrophoretic fluid (24) that includes electrophoretic particles (26).
• the bistable electrophoretic fluid (24) includes a hydrocarbon solvent and the electrophoretic particles (26) comprise carbon black (optionally functionalized as discussed below).
• the light- collimating layer is at least 20 pm thick (i.e., the distance between the first (12) and second (14) light-transmissive electrode layers).
• the light-collimating layer can be thicker than 20 pm, for example thicker than 30 pm, for example thicker than 50 pm, for example thicker than 70 pm, for example thicker than 100 pm, for example thicker than 150 pm, for example thicker than 200 pm.
• a sealing layer 28
• the elongated chambers (22) are sealed with a sealing layer (28), which may be, for example, a hydrophilic polymer that is incompatible with the bistable electrophoretic fluid (24).
• the first (12) and second (14) light-transmissive electrode layers may be coupled to a source (30) of an electrical potential.
• the source may be, e.g., a battery, a power supply, a photovoltaic, or some other source of electrical potential.
• a controller (not shown) is used to supply a time varying voltage between the first (12) and the second (14) light-transmissive electrode layers
• the first (12) and second (14) light-transmissive electrode layers may be coupled to the source (30) via electrodes, wires, or traces (31).
• the traces (31) may be interrupted with a switch (32) which may be, e.g., a transistor switch.
• the electrical potential between the first (12) and second (14) light-transmissive electrode layers is typically at least one volt, for example at least two volts, for example at least five volts, for example at least ten volts, for example at least 15 volts, for example at least 18 volts, for example at least 25 volts, for example at least 30 volts, for example at least 30 volts, for example at least 50 volts.
• the controller supplies a time varying voltage between 5 volts and 150 volts in magnitude, e.g., between 80 volts and 120 volts in magnitude.
• the electrophoretic particles (26) move toward the suitably biased electrode layer, creating a light- transmission gradient along the height of the elongated chambers (22).
• the source (30) can be decoupled from the electrode layers, turning off the electric potential.
• the electrophoretic particles (26) will remain in the second state of a long period of time, e.g., minutes, e.g., hours, e.g., days, as shown in FIG. 1C.
• the state of the light-collimating film (10) can be reversed by driving the collected electrophoretic particles (26) away from the electrode with a reverse polarity voltage (not shown) to achieve FIG. 1D.
• a reverse polarity voltage not shown
• the state of FIG. 1D is also stable.
• the electrophoretic particles (26) can be driven past this distributed state and toward the second light-transmissive electrode (14) with application of the reverse-polarity voltage from FIG. 1B, as shown in FIG. 1E.
• the electrophoretic particles (26) will collect adjacent the second light-transmissive electrode (14) which also results in a wide-viewing angle, as discussed below.
• the wide-angle transmissive state shown in FIG. 1F is also bistable, that is, no power is required to maintain this state. Because the states of FIG. 1C and FIG. 1F both result in wide-angle transmission, it is possible to toggle between the states shown in FIGS. 1A, 1C, 1D, and 1F while maintaining an overall DC balance on the drive electronics. DC balancing the drive electronics reduces charge build- up and extends the life of the system components.
• the internal phase of the electrophoretic medium includes charged pigment particles in a suspending fluid.
• the fluids used in the variable transmission media of the present invention will typically be of low dielectric constant (preferably less than 10 and desirably less than 3).
• Especially preferred solvents include aliphatic hydrocarbons such as heptane, octane, and petroleum distillates such as Isopar ® (Exxon Mobil) or Isane® (Total); terpenes such as limonene, e.g., l-limonene; and aromatic hydrocarbons such as toluene.
• a particularly preferred solvent is limonene, since it combines a low dielectric constant (2.3) with a relatively high refractive index (1.47).
• the index of refraction of the internal phase may be modified with the addition of index matching agents such as Cargille® index matching fluids available from Cargille-Sacher Laboratories Inc. (Cedar Grove, NJ).
• index matching agents such as Cargille® index matching fluids available from Cargille-Sacher Laboratories Inc. (Cedar Grove, NJ).
• the refractive index of the dispersion of particles match as closely as possible that of the encapsulating material to reduce haze. This index-matching is best achieved (when employing commonly-available polymeric encapsulants) when the refractive index of the solvent is close to that of the encapsulant.
• Charged pigment particles may be of a variety of colors and compositions. Additionally, the charged pigment particles may be functionalized with surface polymers to improve state stability. Such pigments are described in U.S. Patent Publication No. 2016/0085132, which is incorporated by reference in its entirety. For example, if the charged particles are of a white color, they may be formed from an inorganic pigment such as Ti02, Zr02, ZnO, A1203, Sb203, BaS04, PbS04 or the like. They may also be polymer particles with a high refractive index (>1.5) and of a certain size (>100 nm) to exhibit a white color, or composite particles engineered to have a desired index of refraction.
• an inorganic pigment such as Ti02, Zr02, ZnO, A1203, Sb203, BaS04, PbS04 or the like.
• They may also be polymer particles with a high refractive index (>1.5) and of a certain size (>100 nm) to exhibit
• Black charged particles they may be formed from Cl pigment black 26 or 28 or the like (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black.
• Other colors may be formed from organic pigments such as Cl pigment PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PBl5:3, PY83, PY138, PY150, PY155 or PY20.
• Clariant Hostaperm Red D3G 70-EDS Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Novoperm Yellow HR-70-EDS, Hostaperm Green GNX, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diarylide yellow or diarylide AAOT yellow. Color particles can also be formed from inorganic pigments, such as Cl pigment blue 28, Cl pigment green 50, Cl pigment yellow 227, and the like.
• the surface of the charged particles may be modified by known techniques based on the charge polarity and charge level of the particles required, as described in U.S. Pat. Nos. 6,822,782, 7,002,728, 9,366,935, and 9,372,380 as well as US Publication No. 2014-0011913, the contents of all of which are incorporated herein by reference in their entirety.
• the particles may exhibit a native charge, or may be charged explicitly using a charge control agent, or may acquire a charge when suspended in a solvent or solvent mixture.
• Suitable charge control agents are well known in the art; they may be polymeric or non polymeric in nature or may be ionic or non-ionic.
• charge control agent may include, but are not limited to, Solsperse 17000 (active polymeric dispersant), Solsperse 9000 (active polymeric dispersant), OLOA 11000 (succinimide ashless dispersant), Unithox 750 (ethoxylates), Span 85 (sorbitan trioleate), Petronate L (sodium sulfonate), Alcolec LV30 (soy lecithin), Petrostep B100 (petroleum sulfonate) or B70 (barium sulfonate), Aerosol OT, polyisobutylene derivatives or poly(ethylene co-butylene) derivatives, and the like.
• internal phases may include stabilizers, surfactants and charge control agents.
• a stabilizing material may be adsorbed on the charged pigment particles when they are dispersed in the solvent. This stabilizing material keeps the particles separated from one another so that the variable transmission medium is substantially non-transmissive when the particles are in their dispersed state.
• dispersing charged particles typically a carbon black, as described above
• a surfactant typically comprises a polar“head group” and a non-polar“tail group” that is compatible with or soluble in the solvent.
• the non-polar tail group be a saturated or unsaturated hydrocarbon moiety, or another group that is soluble in hydrocarbon solvents, such as for example a poly(dialkylsiloxane).
• the polar group may be any polar organic functionality, including ionic materials such as ammonium, sulfonate or phosphonate salts, or acidic or basic groups.
• Particularly preferred head groups are carboxylic acid or carboxylate groups.
• Stabilizers suitable for use with the invention include polyisobutylene and polystyrene.
• dispersants such as polyisobutylene succinimide and/or sorbitan trioleate, and/or 2-hexyldecanoic acid are added.
• the electrophoretic media of the present invention will typically contain a charge control agent (CCA), and may contain a charge director.
• CCA charge control agent
• These electrophoretic media components typically comprise low molecular weight surfactants, polymeric agents, or blends of one or more components and serve to stabilize or otherwise modify the sign and/or magnitude of the charge on the electrophoretic particles.
• the CCA is typically a molecule comprising ionic or other polar groupings, hereinafter referred to as head groups. At least one of the positive or negative ionic head groups is preferably attached to a non-polar chain (typically a hydrocarbon chain) that is hereinafter referred to as a tail group. It is thought that the CCA forms reverse micelles in the internal phase and that it is a small population of charged reverse micelles that leads to electrical conductivity in the very non-polar fluids typically used as electrophoretic fluids.
• Reverse micelles comprise a highly polar core (that typically contains water) that may vary in size from 1 nm to tens of nanometers (and may have spherical, cylindrical, or other geometry) surrounded by the non-polar tail groups of the CCA molecule.
• Reverse micelles have been extensively studied, especially in ternary mixtures such as oil/water/surfactant mixtures.
• An example is the iso-octane/water/ AOT mixture described, for example, in Fayer et al., J. Chem. Phys., 131, 14704 (2009).
• phase In electrophoretic media, three phases may typically be distinguished: a solid particle having a surface, a highly polar phase that is distributed in the form of extremely small droplets (reverse micelles), and a continuous phase that comprises the fluid. Both the charged particles and the charged reverse micelles may move through the fluid upon application of an electric field, and thus there are two parallel pathways for electrical conduction through the fluid (which typically has a vanishingly small electrical conductivity itself).
• the polar core of the CCA is thought to affect the charge on surfaces by adsorption onto the surfaces.
• adsorption may be onto the surfaces of the electrophoretic particles or the interior walls of a microcapsule (or other solid phase, such as the walls of a microcell) to form structures similar to reverse micelles, these structures hereinafter being referred to as hemi-micelles.
• ion exchange between hemi-micelles and unbound reverse micelles can lead to charge separation in which the more strongly bound ion remains associated with the particle and the less strongly bound ion becomes incorporated into the core of a free reverse micelle.
• the ionic materials forming the head group of the CCA may induce ion-pair formation at the electrophoretic particle (or other) surface.
• the CCA may perform two basic functions: charge- generation at the surface and charge-separation from the surface.
• the charge-generation may result from an acid-base or an ion-exchange reaction between some moieties present in the CCA molecule or otherwise incorporated into the reverse micelle core or fluid, and the particle surface.
• useful CCA materials are those which are capable of participating in such a reaction, or any other charging reaction as known in the art.
• the CCA molecules may additionally act as receptors of the photo-excitons produced by the electrophoretic particles when the particles are irradiated with light.
• Non-limiting classes of charge control agents which are useful in the media of the present invention include organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates.
• Useful organic sulfates and sulfonates include, but are not limited to, sodium bis(2-ethylhexyl) sulfosuccinate, calcium dodecylbenzenesulfonate, calcium petroleum sulfonate, neutral or basic barium dinonylnaphthalene sulfonate, neutral or basic calcium dinonylnaphthalene sulfonate, dodecylbenzenesulfonic acid sodium salt, and ammonium lauryl sulfate.
• Useful metal soaps include, but are not limited to, basic or neutral barium petronate, calcium petronate, cobalt, calcium, copper, manganese, magnesium, nickel, zinc, aluminum and iron salts of carboxylic acids such as naphthenic, octanoic, oleic, palmitic, stearic, and myristic acids and the like.
• Useful block or comb copolymers include, but are not limited to, AB diblock copolymers of (A) polymers of 2-(N,N-dimethylamino)ethyl methacrylate quatemized with methyl p-toluenesulfonate and (B) poly(2-ethylhexyl methacrylate), and comb graft copolymers with oil soluble tails of poly(l2-hydroxystearic acid) and having a molecular weight of about 1800, pendant on an oil-soluble anchor group of poly(methyl methacrylate- methacrylic acid).
• Useful organic amides/amines include, but are not limited to, polyisobutylene succinimides such as OLOA 371 or 1200 (available from Chevron Oronite Company LLC, Houston, Tex.), or Solsperse 17000 (available from Lubrizol, Wickliffe, OH: Solsperse is a Registered Trade Mark), and N-vinylpyrrolidone polymers.
• Useful organic zwitterions include, but are not limited to, lecithin.
• Useful organic phosphates and phosphonates include, but are not limited to, the sodium salts of phosphated mono- and di- glycerides with saturated and unsaturated acid substituents.
• Useful tail groups for CCA include polymers of olefins such as poly(isobutylene) of molecular weight in the range of 200 - 10,000.
• the head groups may be sulfonic, phosphoric or carboxylic acids or amides, or alternatively amino groups such as primary, secondary, tertiary or quaternary ammonium groups.
• Charge adjuvants used in the media of the present invention may bias the charge on electrophoretic particle surfaces, as described in more detail below.
• Such charge adjuvants may be Bronsted or Lewis acids or bases.
• Particle dispersion stabilizers may be added to prevent particle flocculation or attachment to the capsule or other walls or surfaces.
• non-aqueous surfactants include, but are not limited to, glycol ethers, acetylenic glycols, alkanolamides, sorbitol derivatives, alkyl amines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.
• the bistability of electrophoretic media can be improved by including in the fluid a polymer having a number average molecular weight in excess of about 20,000, this polymer being essentially non-absorbing on the electrophoretic particles; poly(isobutylene) is a preferred polymer for this purpose.
• a particle with immobilized charge on its surface sets up an electrical double layer of opposite charge in a surrounding fluid.
• Ionic head groups of the CCA may be ion-paired with charged groups on the electrophoretic particle surface, forming a layer of immobilized or partially immobilized charged species.
• a diffuse layer comprising charged (reverse) micelles comprising CCA molecules in the fluid.
• an applied electric field exerts a force on the fixed surface charges and an opposite force on the mobile counter charges, such that slippage occurs within the diffuse layer and the particle moves relative to the fluid.
• the electric potential at the slip plane is known as the zeta potential.
• a light-collimating film (10) can be used to narrow (collimate) light (33) as shown in FIGS. 2A, 2B, and 2C.
• the electrophoretic particles (26) are distributed throughout the elongated chambers (22) resulting in transmission angle qi that is defined by the pitch (A) between elongated chambers (22), the width (W) of each elongated chamber (22), the height (H) of the light-collimating film (10), and the distance from the source of the light (33) to the exiting substrate (in the example of FIG. 2A, substrate (18)).
• the angle qi is roughly defined by the rays X-X’ and Y-Y’, which define the greatest angle from normal that light can leave the source (33) and clear both the top and the bottom of the elongated chamber (22) with electrophoretic particles (26) distributed throughout.
• the electrophoretic particles (26) are driven to the substrate (16) away from the light source (33), and a new transmission angle O3 is established for the rays X-X’ and Y-Y’, as shown in FIG. 2C.
• the new transmission angle O3 will be much wider than Oi, as shown in FIG. 2C, that is, O3 » Oi .
• the effective narrowing of the transmission angle O3 will be a function of the pitch (A) between elongated chambers (22), the width (W) of each elongated chamber (22), and the height (H) of the light-collimating film (10).
• a shadow may be cast by the electrophoretic particles (26) accumulated adjacent to the second substrate (18), this is not observed. It is surmised that there is sufficient scattered light through the light- collimating film (10) to wash out this effect.
• waveforms can be applied between the first and the second light-transmissive electrode layers in order to change the state of the light- collimating film.
• the waveforms can be simple D.C. voltages that are biased to cause the electrophoretic particles (26) to move within the elongated chambers (22).
• a waveform that is simple a D.C. voltage of + Vo can be applied for some time, to, (see WF i) thereby causing the electrophoretic particles to move toward the first electrode (12), as shown in FIG. 3A.
• the process can be reversed by providing a new D.C.
• WF 3 is an alternating voltage waveform that is more negative than positive when integrated over time, thereby resulting in the electrophoretic particles (26) being moved toward the second electrode (14). It has been found empirically that the packing state of the electrophoretic particles (26) is superior when WF 3 is used as compared to a D.C. waveform, such as shown in FIG. 3A. Furthermore, regardless of how the packed state has been addressed, an alternating balanced waveform such as WF 4 is far superior in redistributing the electrophoretic particles (26) within the elongated chambers (22).
• light-collimating films (10) of the invention will provide at least a two-fold reduction in effective viewing angle (as defined by less than 50% percent relative transmission as a function of angle from the normal) in transitioning from wide-transmission angle (FIGS. 2B and 2C) to narrow-transmission angle (FIG. 2A).
• the reduction in viewing area will be greater than two-fold, e.g., three-fold, e.g., four-fold.
• light-collimating film (10) may be useful when simply applied to a pane of glass, e.g., an interior office window, whereby the transmission angle of the glass can be greatly reduced, thereby increasing privacy for the occupants of the office while still allowing a good amount of light to transit through the window.
• a light-collimating film (10) may be incorporated into a liquid crystal display (LCD) stack as shown in FIG. 4.
• FIG. 4 is exemplary, as there are a number of different configurations for LCD stacks.
• a light (33) which is typically one or more light-emitting diodes (LEDs)
• a light-guide plate (34) is directed through the display stack, including the active layer, by a combination of a light-guide plate (34) and a diffuser plate (35).
• a light-collimating film (10) of the type described above.
• the light-collimating film (10) will only allow light to pass to the active layer when that light is travelling within a narrower transmission angle (see FIGS. 2A-2C).
• the light that does pass through the light-collimating film (10) will next proceed through a first polarizing film (36), an active matrix thin film transistor (AM-TFT) array (40) including a plurality of pixel electrodes (42).
• the polarized light passing through the AM-TFT (40) and pixel electrodes (42) will then encounter a liquid crystal layer (44), whereby the polarization of the light can be manipulated by the liquid crystals such that the light will be transmitted through as second polarizing film (37) or rejected.
• the optical state of the liquid crystal layer (44) is altered by providing an electric field between a pixel electrode and the front electrode (45), as is known in the art of LCD displays.
• the light that is transmitted through the light-collimating film (10), AM-TFT (40), pixel electrodes (42), liquid crystal layer (44), and front electrode (45) will then transmit through a color filter array (46) which will only pass the spectrum of color that is to be associated with the underlying pixel electrode (42).
• some amount of light that is of the correct color and the correct polarization (as determined by the liquid crystal layer) will traverse the second polarizing film (37) and be viewed by the viewer.
• Various additional layers of optical adhesives (47) may be included in the stack where needed.
• the stack may also include a protective cover layer (49) which may be, e.g., glass or plastic. Additional elements, such as a capacitive touch-sensitive layer (48) or a digitizer layer (not shown) may also be added to the stack to achieve touch screen capability or writing capability, etc.
• a protective cover layer which may be, e.g., glass or plastic. Additional elements, such as a capacitive touch-sensitive layer (48) or a digitizer layer (not shown) may also be added to the stack to achieve touch screen capability or writing capability, etc.
• an LCD stack may also include a protective cover layer and/or a capacitive touch- sensitive layer.
• the net effect of the LCD stack including a light-collimating film (10) illustrated in FIG. 4 is that it is possible to independently control the effective viewing angle, cp, of light emanating from an LCD display, e.g., a computer monitor, smart phone, data terminal, or other LCD display. Furthermore, because the switching medium is bistable, the device can remain in a“wide” or“narrow” state virtually indefinitely. In advanced embodiments, the amount of narrowing can be adjusted by controlling the relative amount of pigment that is driven toward the viewing side of the elongated chambers. The effective viewing angle can be adjusted completely independent of the state of the LCD. That is, it is not necessary to power down the monitor to switch between a privacy and non-privacy mode.
• FIGS. 5A-5C The variation in effective viewing angle, cp, for an LCD display stack is illustrated in FIGS. 5A-5C.
• the electrophoretic particles (26) are dispersed throughout the elongated chambers (22), rays having a transmission angle qi can travel through the liquid crystal material and color filter material, resulting in an LCD image that is viewable within an effective viewing angle, cp l? as shown in FIG. 5A.
• Viewer #1 the user
• Viewer #2 is outside of the effective viewing angle, and cannot see what is on the LCD screen. That is, Viewer #1 is experiencing a cone of privacy.
• FIG. 6 An exploded view of the sealing layer (28) is shown in FIG. 6.
• the sealing layer (28) seals a top portion of the elongated chamber (22) as shown in the exploded view in order to hold the bistable electrophoretic fluid (24). This may be achieved by under- filling the elongated chamber (22) with bistable electrophoretic fluid (24) and then overcoating the most full elongated chambers (22) with the sealing formulation (discussed below).
• the sealing composition may be dispersed in the bistable electrophoretic fluid (24) at the time of filling, but designed with the correct hydropholicity and density to cause the sealing formulation to rise to the top of the elongated chamber (22) whereby it is hardened, e.g., using light, heat, or exposure to an activating chemical agent.
• the elongated chambers (22) may be filled to the top and the sealing layer spread over the entirety of the top of the light- transmissive polymer (20), thereby sealing the bistable electrophoretic fluid (24) within the elongated chambers.
• Examples of essential components in a sealing composition for the sealing layer may include, but are not limited to, thermoplastic or thermoset and their precursor thereof. Specific examples may include materials such as monofunctional acrylates, monofunctional methacrylates, multifunctional acrylates, multifunctional methacrylates, polyvinyl alcohol, polyacrylic acid, cellulose, gelatin or the like. Additives such as a polymeric binder or thickener, photoinitiator, catalyst, vulcanizer, filler, colorant or surfactant may be added to the sealing composition to improve the physico-mechanical properties and the light-collimating film.
• the sealing composition may be a water soluble polymer with water as the sealing solvent.
• suitable water soluble polymers or water soluble polymer precursors may include, but are not limited to, polyvinyl alcohol; polyethylene glycol, its copolymers with polypropylene glycol, and its derivatives, such as PEG-PPG-PEG, PPG-PEG, PPG-PEG-PPG; poly(vinylpyrrolidone) and its copolymers such as poly(vinylpyrrolidone)/vinyl acetate (PVP/VA); polysaccharides such as cellulose and its derivatives, poly(glucosamine), dextran, guar gum, and starch; gelatin; melamine-formaldehyde; poly(acrylic acid), its salt forms, and its copolymers; poly(methacrylic acid), its salt forms, and its copolymers; poly(maleic acid), its salt forms, and its copolymers; poly(2-dimethyla
• the sealing material may also include a water dispersible polymer with water as a formulating solvent.
• suitable polymer water dispersions may include polyurethane water dispersion and latex water dispersion.
• Suitable latexes in the water dispersion include polyacrylate, polyvinyl acetate and its copolymers such as ethylene vinyl acetate, and polystyrene copolymers such as polystyrene butadiene and polystyrene/acrylate.
• Examples of additional components which may be present, for example in an adhesive composition may include, but are not limited to, acrylics, styrene-butadiene copolymers, styrene-butadiene- styrene block copolymers, styrene-isoprene-styrene block copolymers, polyvinylbutyral, cellulose acetate butyrate, polyvinylpyrrolidone, polyurethanes, polyamides, ethylene-vinylacetate copolymers, epoxides, multifunctional acrylates, vinyls, vinylethers, and their oligomers, polymers and copolymers.
• Adhesive layers may also contain polyurethane dispersions and water soluble polymer selected from the group consisting of polyvinyl alcohol; polyethylene glycol and its copolymers with polypropylene glycol; poly(vinylpyrolidone) and its copolymers; polysaccharides; gelatin; poly(acrylic acid), its salt forms, and its copolymers; poly(methacrylic acid), its salt forms, and its copolymers; poly(2- dimethylaminoethyl methacrylate); poly(2-ethyl-2-oxazoline); poly(2-vinylpyridine); poly(allylamine); polyacrylamide; polymethacrylamide; and a cationic polymer functionalized with quaternary ammonium groups.
• Adhesive layers may be post cured by, for example, heat or radiation such as UV after lamination.
• the edge seal (51) may include any of the sealing compositions described above.
• the edge seal (51) may be continuous around the light-collimating layer (10) and substrate (53), or the edge seal (51) may only cover a portion of the stack, e.g., only the outer edge of the light-collimating layer (10).
• the edge seal (51) may include an additional protective layer, e.g., a layer that is impermeable to water, e.g., clear polyethylene.
• the protective layer may provide moisture or gas barrier properties.
• the edge of the protective layer and or edge seal may be sealed with a thermal or UV curable or thermal activated edge seal material that provides moisture or gas barrier properties.
• the edge seal is sandwiched by two protective substrates.
• the edge seal (51) will actually incase the entire stack, thereby creating a sealed assembly. While not shown, it is understood that one or more electrical connections may have to traverse the edge seal (51) to provide an electrical connection to the first (12) and second (14) electrodes. Such connections may be provided by a flexible ribbon connector.
• FIG. 6 illustrates how a light-collimating layer (10) can be laminated onto the substrate (53) such as glass or another clear durable material. While it is not shown in FIG. 6, it is noted that the light- collimating layer (10) may be protected on both top and bottom with a substrate. The two substrates may be different or the same, for example, a first substrate may be glass and a second substrate may be polyethylene. An edge seal (51) may extend around both top and bottom substrates and the light-collimating layer (10) between substrates.
• an optical adhesive (52) such as available from Delo Adhesives, is used to bond the light-collimating layer (10) to the substrate(s) (53).
• a light-collimating layer (10) may be coated with a combination of an optical adhesive (52) and a release sheet (54) whereby the light- collimating layer (10) with release sheet (54) can be rolled-up and transported to an assembly facility where it will be cut to size. Prior to being deployed, the release sheet (54) can be removed, and the light-collimating layer (10) can be attached directly to the substrate (53), as illustrated in FIG. 7.
• the substrate may be any clear surface for which light collimation is desired, such as a conference room window, automotive glass, or a diffuser in an LCD stack.
• a light collimating film can be produced using a roll-to-roll process as illustrated in FIG. 8, and described in detail in US 9,081,250. As shown in FIG. 8, the process involves a number of steps: In the first step a layer (60) of an embossing composition, e.g., a thermoplastic, thermoset, or a precursor thereof, optionally with a solvent, is deposited on a conductive transparent film (61), such as a film of polyethylene terephthalate (PET) including a layer of indium-tin oxide (PET-ITO).
• PET polyethylene terephthalate
• PET-ITO indium-tin oxide
• a primer layer i.e., an electrode protection layer
• the layer of embossing composition may be used to increase the adhesion between the layer of embossing composition and the supporting layer, which may be the PET. Additionally, an adhesion promoter may be used in the primer layer to improve adhesion to the supporting layer.
• the layer (60) is embossed at a temperature higher than the glass transition temperature of the layer material by a pre-pattemed embossing tool (62), the fabrication of which is described below.
• the primer and/or adhesion promoter may be adjusted to decrease adhesion to the embossing tool (62).
• the patterned layer (60) is released from the embossing tool (62) preferably during or after it is hardened, e.g., by cooling.
• the characteristic pattern of the elongated chambers (as described above) is now established.
• the elongated chambers (63) are filled with a bistable electrophoretic fluid (64), described above.
• the bistable electrophoretic fluid will include a sealing composition that is incompatible with the electrophoretic fluid (64) and has a lower specific gravity than the solvent and the pigment particles in the electrophoretic fluid (64).
• the sealing composition will rise to the top of the elongated chambers (63), whereby it can be hardened in subsequent steps.
• the sealing composition may be overcoated after the elongated chambers (63) are filled with the electrophoretic fluid (64).
• the elongated chambers (63) filled with electrophoretic fluid (64) are sealed by hardening the sealing composition, for example with UV radiation (65), or by heat, or moisture.
• the sealed elongated chambers are laminated to a second transparent conductive film (66), which may be pre-coated with an optically clear adhesive layer (67), which may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture, or radiation curable adhesive.
• an optically clear adhesive layer which may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture, or radiation curable adhesive.
• optically- clear adhesive examples include acrylics, styrene-butadiene copolymers, styrene-butadiene- styrene block copolymers, styrene-isoprene-styrene block copolymers, polyvinylbutyal, cellulose acetate butyrate, polyvinylpyrrolidone, polyurethanes, polyamides, ethylene-vinylacetate copolymers, epoxides, multifunctional acrylates, vinyls, vinylethers, and their oligomers, polymers, and copolymers.
• the finished sheets of switchable light-collimating film may be cut, e.g., with a knife edge (69), or with a laser cutter.
• an eighth step including laminating another optically-clear adhesive and a release sheet may be performed on the finished switchable light-collimating film so that the film can be shipped in section sheets or rolls and cut to size when it is to be used, e.g., for incorporation into a display, a window, or other device/substrate.
• the embossing tool (62) may be prepared by a photoresist process followed by either etching or electroplating. It is then coated with a layer of photoresist and exposed to UV. A mask is placed between the UV and the layer of photoresist. In some embodiments, the unexposed or exposed areas are then removed by washing them with an appropriate organic solvent or aqueous solution. The remaining photoresist is dried and sputtered again with a thin layer of seed metal. The master is then ready for electroforming. A typical material used for electroforming is nickel cobalt. Alternatively, the master can be made of nickel by nickel sulfamate electroforming or electroless nickel deposition.
• the floor of the embossing tool is typically between 50 and 5000 microns thick.
• the master can also be made using other microengineering techniques including e-beam writing, dry etching, chemical etching, laser writing or laser interference as described in“Replication techniques for micro-optics”, SPIE Proc. Vol. 3099, pp 76-82 (1997).
• the embossing tool can be made by photomachining using plastics, ceramics or metals. Several methods for embossing tool production are described in greater detail below. [Para 79]
• Figures 9A and 9B illustrate the embossing process with an embossing tool (111), with a three-dimensional microstructure (circled) on its surface. As shown in FIGS.
• the embossing tool (111) is applied to the embossing composition (112) of at least 20 pm thick, e.g., at least 40 pm thick, e.g., at least 50 pm thick, e.g., at least 60 pm thick, e.g., at least 80 pm thick, e.g., at least 100 pm thick, e.g., at least 150 pm, e.g., at least 200 pm thick, e.g., at least 250 pm thick.
• the embossing composition is cured (e.g., by radiation), or the hot-embossable material becomes embossed by heat and pressure
• the embossed material is released from the embossing tool (see Figure 9B), leaving behind elongated chambers of the requisite dimensions, e.g., wherein a height of the elongated chambers is equal to or less than the thickness of the collimating layer (embossing composition), and wherein a width of the elongated chambers is between 9 pm and 150 pm, and a length of the chambers is between 200 pm and 5 mm.
• an object may be formed on a stack of layers, and in this case, if the adhesion between any two of the adjacent layers is weaker than the adhesion between the cured or hot embossed material and the surface of the embossing tool, the release process of the cured or hot embossed material from the embossing tool could cause a break-down between the two layers.
• Suitable hydrophilic compositions for forming the embossing layer or supporting layer may comprise a polar oligomeric or polymeric material.
• a polar oligomeric or polymeric material may be selected from the group consisting of oligomers or polymers having at least one of the groups such as nitro (-N0 2 ), hydroxyl (-OH), carboxyl (-COO), alkoxy (-OR wherein R is an alkyl group), halo (e.g., fluoro, chloro, bromo or iodo), cyano (-CN), sulfonate (-S0 3 ) and the like.
• the glass transition temperature of the polar polymer material is preferably below about 100°C and more preferably below about 60°C.
• suitable polar oligomeric or polymeric materials may include, but are not limited to, polyvinyl alcohol, polyacrylic acid, poly(2-hydroxylethyl methacrylate), polyhydroxy functionalized polyester acrylates (such as BDE 1025, Bomar Specialties Co, Winsted, CT) or alkoxylated acrylates, such as ethoxylated nonyl phenol acrylate (e.g., SR504, Sartomer Company), ethoxylated trimethylolpropane triacrylate (e.g., SR9035, Sartomer Company) or ethoxylated pentaerythritol tetraacrylate (e.g., SR494, from Sartomer Company).
• the embossing tool (111) maybe used directly to emboss the composition (112).
• the embossing tool (111) is mounted on a plain drum to allow rotation of the embossing sleeve over the embossing composition (112).
• the embossing drum or sleeve (121) is usually formed of a conductive material, such as a metal (e.g., aluminum, copper, zinc, nickel, chromium, iron, titanium, cobalt or the like), an alloy derived from any of the aforementioned metals, or stainless steel.
• a metal e.g., aluminum, copper, zinc, nickel, chromium, iron, titanium, cobalt or the like
• an alloy derived from any of the aforementioned metals or stainless steel.
• Different materials may be used to form a drum or sleeve.
• the center of the drum or sleeve may be formed of stainless steel and a nickel layer is sandwiched between the stainless steel and the outermost layer which may be a copper layer.
• the embossing drum or sleeve (121) may be formed of a non- conductive material with a conductive coating or a conductive seed layer on its outer surface, as shown in FIG. 10.
• a photosensitive material (122) on the outer surface of a drum or sleeve (21), as shown in step B of FIG. 10 precision grinding and polishing may be used to ensure smoothness of the outer surface of the drum or sleeve.
• a photosensitive material (122), e.g., a photoresist, can then be coated on the outer surface of the drum or sleeve (121).
• the photosensitive material may be of a positive tone, negative tone or dual tone.
• the photosensitive material may also be a chemically amplified photoresist.
• the coating may be carried out using dip, spray or ring coating. After drying and/or baking, the photosensitive material may be subjected to exposure, as shown in step C of FIG. 10, e.g., by exposing the photosensitive material to a light source.
• the photosensitive material (122) can be a dry film photoresist that is laminated onto the outer surface of the drum or sleeve (121). When a dry film is used, it is also exposed to a light source as described.
• a suitable light source e.g., IR, UV, e-beam or laser, is used to expose the photosensitive material coated or a dry film photoresist (122) laminated on the drum or sleeve (121).
• the light source can be a continuous or pulsed light.
• the exposure can be step-by-step, continuous or a combination thereof.
• the photosensitive material (122) may be subjected to post-exposure treatment, e.g., baking, before development. Depending on the tone of the photosensitive material, either exposed or un-exposed areas will be removed by using a developer. After development, the drum or sleeve with a patterned photosensitive material
• the thickness of the patterned photosensitive material is preferably greater than the depth or height of the three-dimensional microstructure to be formed.
• a metal or alloy e.g., nickel, cobalt, chrome, copper, zinc or an alloy derived from any of the aforementioned metals
• the plating material (126) is deposited on the outer surface of the drum or sleeve in areas that are not covered by the patterned photosensitive material. The deposit thickness is preferably less than that of the photosensitive material, as shown in step E of FIG. 10.
• the thickness variation of the deposit over the whole drum or sleeve area can be controlled to be less than 1%, by adjusting plating conditions, e.g., the distance between the anode and the cathode (i.e., drum or sleeve) if electroplating is used, the rotation speed of the drum or sleeve and/or circulation of the plating solution.
• plating conditions e.g., the distance between the anode and the cathode (i.e., drum or sleeve) if electroplating is used, the rotation speed of the drum or sleeve and/or circulation of the plating solution.
• the thickness variation of the deposit over the entire surface of the drum or sleeve may be controlled by inserting a non-conductive thickness uniformer between a cathode (i.e., the drum or sleeve) and an anode, as described in US Patent No. 8,114,262, the content of which is incorporated herein by reference in its entirety.
• the patterned photosensitive material (125) can be stripped by a stripper (e.g., an organic solvent or aqueous solution).
• a precision polishing may be optionally employed to ensure acceptable thickness variation and degree of roughness of the deposit (126) over the entire drum or sleeve.
• Step F of FIG. 10 shows a cross-section view of an embossing drum or sleeve with a three-dimensional pattern microstructure formed thereon.
• a three-dimensional microstructure may be formed on a flat substrate, as shown in FIG. 11.
• a photosensitive material (142) is coated on a substrate layer (141) (e.g., a glass substrate).
• the photosensitive material (142) may be of a positive tone, negative tone or dual tone.
• the photosensitive material (142) may also be a chemically amplified photoresist.
• the coating may be carried out using dip, spray, slot die, or spin coating. After drying and/or baking, the photosensitive material is subjected to exposure to a suitable light source (not shown) through a photomask (not shown).
• the photosensitive material (142) can be a dry film photoresist (which is usually commercially available) that is laminated onto the substrate (141). The dry film is also exposed to a light source as described above.
• Step B of FIG. 11 after exposure, depending on the tone of the photosensitive material, either the exposed or un-exposed areas of the photosensitive material will be removed by using a developer. After development, the substrate layer (141) with the remaining photosensitive material (142) may be subjected to baking or blanket exposure before Step C. The thickness of the remaining photosensitive material should be the same as the depth or height of the three-dimensional microstructure to be formed.
• an electrical conductive seed layer (143) is coated over the remaining photosensitive material (142) and the substrate (141) in areas not occupied by the photosensitive material.
• the electrical conductive seed layer is usually formed of silver, however other conductive materials, such as gold or nickel may also be used.
• Step D a metal or alloy (144) (e.g., nickel, cobalt, chrome, copper, zinc, or an alloy derived from any of the aforementioned metals) is electroplated and/or electroless plated onto the surface covered by electrical conductive seed layer and the plating process is carried out until there is enough plated material thickness (h) over the patterned photosensitive material.
• the thickness (h) in Step D of FIG. 11 is preferably 25 to 5000 microns, and more preferably 25 to 1000 microns.
• the plated material (144) is separated from the substrate layer (141) which is peeled off.
• the photosensitive material (142) along with the electrical conductive seed layer (143) is removed.
• the photosensitive material may be removed by a stripper (e.g., an organic solvent or aqueous solution).
• the electrical conductive seed layer (143) may be removed by an acidic solution (e.g., sulfuric/nitric mixture) or commercially available chemical strippers, leaving behind only a metal sheet (144) having a three- dimensional structure on one side and being flat on the other side.
• a precision polishing may be applied to the metal sheet (144), after which the flat shim may be used directly for embossing, or it may be mounted on (i.e., wrapped over) a drum with the three-dimensional microstructure on the outer surface to form an embossing tool.
• a precious metal or alloy thereof is finally coated over the entire surface of the embossing tool, as described above. As stated above, gold or its alloy is preferred over other precious metals and alloys due to its lack of reactivity.
• Step E A further alternative method is demonstrated in FIG. 12. This method is similar to that of FIG. 11, but simplified. Instead of an electrical conductive seed layer such as silver, a layer of precious metal or alloy thereof (153) is simply coated over the photosensitive material (152). As stated above, gold or its alloy is preferred. Consequently, in Step E, after the plated material (154) is separated from the substrate (151), only the photosensitive material (152) is removed, the gold or alloy coating (153) remains with the metal sheet (154) with a three-dimensional structure on one side and being flat on the other side.
• an electrical conductive seed layer such as silver
• a layer of precious metal or alloy thereof (153) is simply coated over the photosensitive material (152).
• gold or its alloy is preferred. Consequently, in Step E, after the plated material (154) is separated from the substrate (151), only the photosensitive material (152) is removed, the gold or alloy coating (153) remains with the metal sheet (154) with a three-dimensional structure on one side and being flat on the other side.
• components in a composition for forming the collimating layer may include, but are not limited to, thermoplastic or thermoset materials or a precursor thereof, such as multifunctional vinyls including, but not limited to, acrylates, methacrylates, allyls, vinylbenzenes, vinylethers, multifunctional epoxides and oligomers or polymers thereof, and the like. Multifunctional acrylate and oligomers thereof are often used. A combination of a multifunctional epoxide and a multifunctional acrylate is also useful to achieve desirable physico-mechanical properties of the collimating layer. A low Tg (glass transition temperature) binder or crosslinkable oligomer imparting flexibility, such as urethane acrylate or polyester acrylate, may also be added to improve the flexure resistance of the embossed privacy layers.
• thermoplastic or thermoset materials or a precursor thereof such as multifunctional vinyls including, but not limited to, acrylates, methacrylates, allyls, vinylbenzenes, vinylethers
• compositions for a collimating layer may comprise a polar oligomeric or polymeric material.
• a polar oligomeric or polymeric material may be selected from the group consisting of oligomers or polymers having at least one of the groups such as nitro (— N0 2 ), hydroxyl (— OH), carboxyl (— COO), alkoxy (— OR wherein R is an alkyl group), halo (e.g., fluoro, chloro, bromo or iodo), cyano (— CN), sulfonate (— S03) and the like.
• the glass transition temperature of the polar polymer material is preferably below about 100° C, and more preferably below about 60° C.
• Suitable polar oligomeric or polymeric materials may include, but are not limited to, polyhydroxy functionalized polyester acrylates (such as BDE 1025, Bomar Specialties Co, Winsted, Conn.) or alkoxylated acrylates, such as ethoxylated nonyl phenol acrylate (e.g., SR504, Sartomer Company), ethoxylated trimethylolpropane triacrylate (e.g., SR9035, Sartomer Company) or ethoxylated pentaerythritol tetraacrylate (e.g., SR494, from Sartomer Company).
• polyhydroxy functionalized polyester acrylates such as BDE 1025, Bomar Specialties Co, Winsted, Conn.
• alkoxylated acrylates such as ethoxylated nonyl phenol acrylate (e.g., SR504, Sartomer Company), ethoxylated trimethylolpropane triacrylate (e.g.,
• the collimating layer composition may comprise (a) at least one difunctional UV curable component, (b) at least one photoinitiator, and (c) at least one mold release agent.
• Suitable difunctional components may have a molecular weight higher than about 200. Difunctional acrylates are preferred and difunctional acrylates having a urethane or an ethoxylated backbone are particularly preferred.
• suitable difunctional components may include, but are not limited to, diethylene glycol diacrylate (e.g., SR230 from Sartomer), triethylene glycol diacrylate (e.g., SR272 from Sartomer), tetraethylene glycol diacrylate (e.g., SR268 from Sartomer), polyethylene glycol diacrylate (e.g., SR295, SR344 or SR610 from Sartomer), polyethylene glycol dimethacrylate (e.g., SR603, SR644, SR252 or SR740 from Sartomer), ethoxylated bisphenol A diacrylate (e.g., CD9038, SR349, SR601 or SR602 from Sartomer), ethoxylated bisphenol A dimethacrylate (e.g., CD540, CD542, SR101, SR150, SR348, SR480 or SR541 from Sartomer), and urethane diacrylate (e.g.,
• Suitable photoinitiators may include, but are not limited to, bis-acyl-phosphine oxide, 2-benzyl-2-(dimethylamino)-l-[4-(4- morpholinyl)phenyl]-l-butanone, 2,4,6-trimethylbenzoyl diphenyl phosphine oxide, 2- isopropyl-9H-thioxanthen-9-one, 4-benzoyl-4'-methyldiphenylsulphide and 1 -hydroxy- cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl- 1 -phenyl-propan- 1 -one, 1 - [4-(2- hydroxyethoxy)-phenyl] -2-hydroxy-2-methyl- 1 -propane- 1 -one, 2,2-dimethoxy- 1,2- diphenylethan- 1 -one or 2-methyl- 1 [4-(methylthio)phenyl] -2-morpholinopropan- 1 -one.
• Suitable mold release agents may include, but are not limited to, organomodified silicone copolymers such as silicone acrylates (e.g., Ebercryl 1360 or Ebercyl 350 from Cytec), silicone polyethers (e.g., Silwet 7200, Silwet 7210, Silwet 7220, Silwet 7230, Silwet 7500, Silwet 7600 or Silwet 7607 from Momentive).
• the composition may further optionally comprise one or more of the following components, a co-initiator, monofunctional UV curable component, multifunctional UV curable component or stabilizer.
• the length (L) of an elongated chamber is typically at least twice the width (W) of the elongated chamber, e.g., at least three times the width of the elongated chamber, e.g., at least four times the width of the elongated chamber, e.g., at least five times the width of the elongated chamber, e.g., at least ten times the width of the elongated chamber.
• the height (H) (out of the plane of the page in FIGS.
• each elongated chamber 13 and 14 is equal to or less than the thickness of the collimating layer.
• the width of each elongated chamber is between 9 pm and 150 pm.
• the length of each elongated chamber is between 200 pm and 5 mm.
• FIG. 13 the overall transmission of FIG. 13 is lower than the overall transmission of FIG. 14.
• there is less“leakage” of non-collimated light in FIG. 13 because there are fewer off-axis pathways for incident light to travel past the elongated chambers.
• the elongated chambers are formed in rows and columns (as viewed from above).
• the gaps between adjacent elongated chambers in the first row are offset horizontally from the gaps between adjacent elongated chambers in the second row in both FIG 13 and FIG. 14.
• the gap width “G” between adjacent elongated chambers within the same row is less than 30 pm, e.g., less than 25 pm, e.g., less than 20 pm, e.g., less than 15 pm, e.g., less than 10 pm.
• the gaps between adjacent elongated chambers in successive rows may be offset by at least 1 pm, e.g., at least 2 pm, e.g., at least 3 pm, e.g., at least 5 pm.
• the entire gap of a first row is spanned by the elongated chamber of a second row, as shown in FIG. 14.
• Encapsulated electrophoretic media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically- mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes.
• the charged particles and the fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film.
• Electrophoretic particles, fluids and fluid additives see for example U.S. Patents Nos. 7,002,728 and 7,679,814; as well as U.S. Patent Applications Publication No. 2016/0170106;
• Capsules, binders and encapsulation processes see for example U.S. Patents Nos. 6,922,276 and 7,411,719; as well as U.S. Patent Applications Publication No. 2011/0286081;
• Microcell structures, wall materials, and methods of forming microcells see for example United States Patents Nos.
• a backplane containing an array of pixel electrodes and an appropriate arrangement of conductors to connect the pixel electrodes to drive circuitry, is prepared.
• the substrate having the capsule/binder layer thereon is laminated to the backplane using a lamination adhesive.
• the backplane is itself flexible and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate.
• both electrodes are flexible, thereby allowing the constructed electrophoretic display to be flexible.
• the obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive. Similar manufacturing techniques can be used with other types of electro-optic displays.
• a microcell electrophoretic medium may be laminated to a backplane or flexible electrode in substantially the same manner as an encapsulated electrophoretic medium.
• U.S. Patent No. 6,982,178 describes a method of assembling a solid electro-optic display (including an encapsulated electrophoretic display) which is well adapted for mass production.
• this patent describes a so-called "front plane laminate" ("FPL") which comprises, in order, a light-transmissive electrically-conductive layer; a layer of a solid electro optic medium in electrical contact with the electrically-conductive layer; an adhesive layer; and a release sheet.
• FPL front plane laminate
• the light-transmissive electrically-conductive layer will be carried on a light-transmissive substrate, which is preferably flexible, in the sense that the substrate can be manually wrapped around a drum (say) 10 inches (254 mm) in diameter without permanent deformation.
• the term "light-transmissive" is used in this patent and herein to mean that the layer thus designated transmits sufficient light to enable an observer, looking through that layer, to observe the change in display states of the electro-optic medium, which will normally be viewed through the electrically-conductive layer and adjacent substrate (if present); in cases where the electro-optic medium displays a change in reflectivity at non-visible wavelengths, the term “light-transmissive” should of course be interpreted to refer to transmission of the relevant non-visible wavelengths.
• the substrate will typically be a polymeric film, and will normally have a thickness in the range of about 1 to about 25 mil (25 to 634 mih), preferably about 2 to about 10 mil (51 to 254 pm).
• the electrically-conductive layer is conveniently a thin metal or metal oxide layer of, for example, aluminum or ITO, or may be a conductive polymer.
• PET poly(ethylene terephthalate)
• PET poly(ethylene terephthalate)
• Mylar is a Registered Trade Mark
• E.I. du Pont de Nemours & Company Wilmington DE, and such commercial materials may be used with good results in the front plane laminate.
• Assembly of an electrophoretic display using such a front plane laminate may be effected by removing the release sheet from the front plane laminate and contacting the adhesive layer with the backplane under conditions effective to cause the adhesive layer to adhere to the backplane, thereby securing the adhesive layer, layer of electrophoretic medium and electrically-conductive layer to the backplane.
• This process is well-adapted to mass production since the front plane laminate may be mass produced, typically using roll-to-roll coating techniques, and then cut into pieces of any size needed for use with specific backplanes.
• impulse is used herein in its conventional meaning of the integral of voltage with respect to time.
• bistable electrophoretic media act as charge transducers, and with such media an alternative definition of impulse, namely the integral of current over time (which is equal to the total charge applied) may be used.
• the appropriate definition of impulse should be used, depending on whether the medium acts as a voltage-time impulse transducer or a charge impulse transducer.
• an encapsulated electrophoretic medium typically comprises electrophoretic capsules disposed in a polymeric binder, which serves to form the discrete capsules into a coherent layer.
• the continuous phase in a polymer-dispersed electrophoretic medium, and the cell walls of a microcell medium serve similar functions. It has been found by E Ink researchers that the specific material used as the binder in an electrophoretic medium can affect the electro-optic properties of the medium. Among the electro-optic properties of an electrophoretic medium affected by the choice of binder is the so-called "dwell time dependence". As discussed in the U.S. Patent No.
• DTD dwell time dependence
• U.S. Patent Application Publication No. 2005/0107564 describes an aqueous polyurethane dispersion comprising a polyurethane polymer comprising the reaction product of: (a) an isocyanate terminated prepolymer comprising the reaction product of (i) at least one polyisocyanate comprising a,a,a,a-tetramethylxylene diisocyanate [systematic name l.3-bis(l- isocyanato-l-methylethyl)benzene; this material may hereinafter be called "TMXDI"]; (ii) at least one difunctional polyol comprising polypropylene glycol, and (iii) an isocyanate reactive compound comprising an acid functional group and at least two isocyanate reactive groups selected from a hydroxy, a primary amino, a secondary amino, and combinations thereof; (b) a neutralizing agent comprising a tertiary amino group; (c) a monofunctional chain terminating agent;
• the present invention can provide a switchable light-collimating film and devices that incorporate switchable light-collimating films.
• the invention provides light-collimating films that are bistable and able to maintain wide and narrow viewing conditions with no additional energy input.

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